Various medical devices, e.g., implantable drug delivery devices, have one or more needle receiving ports (e.g. to access a reservoir or a catheter) which may include a needle access hole dimensioned to deny access to needles larger than a predetermined diameter. For example, U.S. Pat. No. 6,293,922 describes a port comprised of a conical depression leading to a central access hole which has “a diameter substantially the same as the predetermined diameter for preventing access to the septum” by oversized hypodermic needles. Needles having diameters smaller than the predetermined diameter are able to pass through the access hole and septum to exchange fluid with the reservoir or catheter. Generally, a physical stop, e.g., a pad made of firm, biocompatible polymer material, is inserted below the septum to engage the needle's tip to limit penetration and provide a tactile feedback to the user advising that the tip of the needle has bottomed. Unfortunately, however, the fragile needle tip can sometimes engage a surface which may cause it to curl up like a fish hook. The hook portion can then damage the septum when the needle is withdrawn from the port.
Implantable medical device ports may also incorporate some type of filtering means, e.g., a sintered or mesh material, to prevent the introduction of particulate matter into the reservoir or catheter.